1. Field of the Invention
The present invention relates to an ink suited for an ink-jet recording method of carrying out the recording by causing droplets to fly from orifices of a recording head, and an ink-jet recording process employing the same. More particularly, it is concerned with ink for ink-jet recording that can achieve a superior high frequency response and ejection stability and also a superior print quality and fixing performance, and also an ink-jet recording process employing the same.
2. Description of the Related Art
In ink-jet recording methods, ink droplets are formed according to various ink ejection methods, and a part, or the whole, thereof is adhered on a recording medium such as paper, coated paper, plastic film, cloth, etc. to effect the recording. As the ink used for such an ink-jet recording method, there have been known and used those obtained by dissolving or dispersing every sort of dyes or pigments in a liquid medium.
What are required in such ink in relation also to the recording medium are the performances as follows:
(1) no feathering occurs on the printed part on the recording medium;
(2) ink can be immediately dried on the recording medium (including the case when dried by absorption);
(3) nozzles of a printer may not be clogged even when the printing is interrupted for a while;
(4) ink can achieve a good ink ejection frequency response matched to the printing speed of a printer;
(5) ink has high storage stability;
(6) ink is highly safe; etc.
To satisfy the various required performances as mentioned above, a variety of studies has been carried out in respect of additives such as organic solvents and surface active agents as the liquid medium, or further in respect of the values for properties such as viscosity and surface tension of ink, and considerable effect has been realized depending on what performance is required.
However, at present, noted as strongly required performances in using the above conventional ink are the following two points, on which intensive studies have also been made. That is to say;
(1) the development of the ink that can be adapted to a high speed recording; and
(2) the development of the ink that may not cause any feathering on a recording medium on which fibers are exposed.
Firstly, in respect of the improvement in the printing speed of a printer, a greater part of the approaches thereto have been made from the standpoint of mechanics such as head construction, and in fact not so many studies have been made on the improvement in the ejection frequency response attributable to the ink.
In general, the frequency response can be improved with decrease in the viscosity of ink, accompanied, however, with a lowering of the stability of ejection. Accordingly, in the present state of the art, it is difficult to develop such ink that can improve the frequency response while retaining the ejection stability. In particular, there is caused the problem such that the frequency response and the ejection stability becomes inferior under the condition of the driving at a frequency of 1 kHz or more. This tendency may become more remarkable with increase in the drive frequency to 2 kHz, 4 kHz and so on, raising a serious problem particularly in the ink-jet recording method utilizing a piezoelectric device or a heat energy.
Secondly, in respect of the feathering or the drying performance on the recording medium on which the fibers are exposed, there may be caused the problem such that the feathering of ink occurs along the fibers of the paper particularly when the printing was performed on ordinary paper such as copying paper, bond paper and report paper used as the recording medium, or a sizing agent contained in the ordinary paper affects the fixing performance to make it insufficient.
Thus, attempts have been already made for a method of carrying out the recording with use of ink whose pH was controlled to make the ink strongly alkaline for the purpose of preventing the feathering and improving the fixing performance (for example, Japanese Patent Laid-open Publication No. 57862/1981), a method of carrying out the recording with use of ink to which a large amount of surface active agent has been added (for example, Japanese Patent Laid-open Publication No. 29546/1980), and so forth. However, the method of carrying out the recording by controlling the pH to make the ink strongly alkaline can be dangerous if the ink is touched by hands, and also has disadvantages such that both the prevention of feathering and the improvement of drying performance can not be favorably achieved for the paper employing a certain kind of the sizing agent. In respect of the method of carrying out the recording with use of the ink to which a large amount of surface active agent has been added, there can be seen the troubles such that the feathering very frequently occurs depending on the kind of paper used, or the ink backward moves from the face of an orifice depending on the conditions for a print head, resulting in no ejection of ink, or, on the contrary, the whole face of the orifice is wetted resulting also in no ejection of ink.